Various electronic devices include integrated circuit (IC) components including any number of capacitors formed therein. Some IC capacitors utilize a multilayer dielectric material between anode and cathode capacitive plates, e.g., an oxide-nitride-oxide (ONO) multilayer dielectric including a silicon nitride layer between a pair of oxide layers. Silicon nitride has a high dielectric constant, and may thus be used to increase the breakdown voltage of the capacitor, while keeping the capacitance the same. Certain conventional IC capacitors, including certain IC capacitors using ONO dielectric may include defects or characteristics that cause failures that result in leakage current in the capacitors, which may cause errors or failures in the capacitors and/or an end product in which the capacitors are included. These defects include defects at one or more edges of the capacitor structure, e.g., due to concentrated electric fields at such edge regions. Further, the incidence of failures resulting from such defects may increase as a function of higher voltage applications.
FIGS. 1A-1B and 2A-2B illustrate two example capacitors implemented by conventional processes and systems, and may suffer from the deficiencies discussed above. Each capacitor shown in FIGS. 1A-1B and 2A-2B includes a pair of conductor plates (e.g., positive plate and negative plate, or anode and cathode) embodied as a pair of conductive poly layers (a poly 2 layer over a poly 1 layer) separated by an oxide-nitride-oxide (ONO) layer. Defects may occur near a lateral edge of the poly 2 layer and underlying ONO layer. This region is circled in each of FIGS. 1A-1B and 2A-2B. It should be understood that in alternative embodiments the capacitor plates may be embodied by any suitable structures or materials other than polysilicon layers.
FIGS. 1A and 1B shows microscope images (e.g., taken using a tunneling electron microscope) of a cross-section of a first conventional capacitor structure 100 that may show signs of failure, and also exemplifies the undesirable properties mentioned above, e.g., errors due to field effects near the lateral edge of the poly 2 layer.
The example capacitor 100 includes a base poly silicon layer 110, an ONO structure (layer stack) 103 including an oxide layer 108, a silicon nitride (also referred to herein simply as nitride) layer 106, another oxide layer 104, and a top poly silicon layer 102. As shown in FIG. 1B, oxide layers 108 and 104 may remain separated at the lateral edge or sidewall of top poly silicon layer 102, and nitride layer 106 may extend to this lateral edge or sidewall. Thus, capacitor 100 may not yet have failed, but may experience unwanted field effects. For example, increasing electric lines at the edge of the capacitor may concentrate the field at point 112, which is represented as a brighter spot in FIG. 1B. Point 112 may include a void in the oxide due to heating in a different plane. This increased electric field may subsequently lead to an error or failure.
FIGS. 2A and 2B shows microscope images (e.g., taken using a scanning electron microscope) of a cross-section of a second conventional capacitor structure 200 that further demonstrates the weakness described due to normal process variations in the silicon nitride layer, resulting in narrow dielectric at the capacitor edge.
As with capacitor 100 shown in FIGS. 1A-1B, capacitor 200 includes a base poly silicon layer 210, an ONO structure 203 (layer stack) including an oxide layer 208, a nitride layer 206, another oxide layer 204, and a top poly silicon layer 202. FIG. 2B illustrates that the capacitor may fail at a much lower voltage than intended. The failure may include a convergence or breakthrough of oxide layers 208 and 204 at point 212, and nitride layer 206 might not extend fully to the sidewall or edge of top poly silicon layer 202. The failure to extend fully to the edge/sidewall, as well as the convergence of oxide layers 208, 204, may be an unintentional result of poor etching or other etching mistakes. Moreover, the failure may result from the high field effects shown in FIGS. 1A and 1B. Oxide layers 208 and 204 and nitride layer 206 may have been etched together, e.g., using an isotropic process wherein the etching is applied straight downward.